This invention relates generally to wheelnuts for mounting wheels on the axles of motor vehicles. More particularly, the wheelnut of this invention is structured to prevent the nut from engaging the wheel with an overload that might cause deformation of the wheel, particularly, in cases where the wheel is made of a metal softer than steel such as aluminum. The majority of wheelnuts include a conical surface which engages the wheel and applies a clamping force to the wheel in response to torque.
The defining characteristic of the majority of wheelnuts is the conical surface. This is the surface through which clamping forces are applied and also the means by which the wheel is centered in the final assembled position. Decades of application and testing has produced a body of engineering knowledge about wheel assembly. Modern wheel assembly methods and controls have been developed as a result of this empirical data.
A certain minimum clamping force is specified for a wheel assembly and a method for determining that this criteria is met at assembly is necessary. In the laboratory this is accomplished with a special fixture and a load sensor that measures this force. In the assembly plant, no practical method of directly measuring this force exists, but torque and torque angle can be measured. An understanding of the relationship between torque and clamp load makes torque and torque angle an appropriate control measurement to ensure proper clamp load. Upper and lower limits are set for torque applied at assembly and torque angle is monitored to detect variance from the normal duration of the torque vs. tension force curve. Extreme variance from the defined norm can indicate a problem in the assembly that could compromise the assembly strength.
Occasionally very high clamp loads are generated (due to any of several variables) that can mean joint failure on an aluminum alloy wheel and no adverse consequence on a steel wheel. The failure is in the inability of the nut seat in the wheel to support this high clamp load, which is a consequence of the lower strength of aluminum. When this occurs, the nut drives through the wheel until clamp load is achieved. The magnitude of nut seat deformation can be judged by the torque angle value, the greater torque angle indicating greater nut seat deformation. Excessive deformation is considered to produce a faulty or unacceptable joint.
This invention provides for a feature on the wheelnut that limits the amount of deformation in the wheel seat, likewise limiting the torque angle at assembly.
The limiting feature in this invention is the provision of a stop surface on the wheelnut which is generally perpendicular to the axis of the nut and intersects the conical surface to thereby preclude the application of torque forces on the wheelnut that overload and deform the wheel in the case of wheels made of softer metals, such as aluminum. Several embodiments of the invention are disclosed and all include this limiting stop surface which limits the clamping force that can be applied to the wheel when it is being mounted on the motor vehicle.
Further features, advantages and innovations will be apparent from the following drawings when taken in connection with the specification and claims.